In a hard-disk drive (HDD), servo data is recorded along tracks formed on a magnetic-recording disk, in which the servo data is readable by a magnetic-recording head flying over the magnetic-recording disk. Consequently, the HDD has an actuator control system that controls an actuator, which causes a relative movement of the magnetic-recording head with respect to the magnetic-recording disk, in correspondence to the read out servo data.
The actuator control system, such as described above, is provided with various countermeasures against periodic disturbances occurring because of various factors. However, such disturbances include those such as vibrations externally imposed on the HDD, those having a frequency that cannot easily be pre-identified, and those having a frequency that fluctuates over time, such that it is difficult to sufficiently suppress such disturbances.